An electronic control system to which the invention may be applied is described in an article entitled "Elektronische Motorsteuerung fuer Kraftfahrzeuge" published in "MTZ" Motortechnische Zeitschrift, year 46, Vol. 4, 1985, published by Franckh'sche Verlagshandlung Stuttgart. In this article, it is explained that electronic engine control (called "EMS" for short) means a system in which the conventional mechanical linkage between the accelerator pedal and the element (the throttle valve in a petrol engine or the regulating rod in a diesel injection pump) determining the engine output is replaced by an electrical connection comprising a pedal travel transducer (potentiometer) actuated by the accelerator pedal and an actuator (servomotor) actuating the said element.
The above article describes in particular a system (now sometimes called "E-gas") in which the servomotor adjusts the throttle valve in carburetor or petrol injection engine. U.S. Pat. Nos. 4,515,125 and 4,509,480 describe supervisory systems of the initially recited kind which are used for electronic diesel control (EDC). The two patent specifications disclose the use of a separate switch for detecting whether or not the accelerator pedal is in its idling position. The EDC performs a "signal-range check" to monitor the occurrence of faults in the operation of the system. Amongst other parameters, the accelerator pedal position is monitored and, for the purpose of the signal-range check, a separate idling switch, actuated when the accelerator pedal is in its idling position, may be used rather than the pedal travel transducer. The purpose of carrying out the signal-range check on the accelerator pedal position is to ensure that appropriate measures are taken by the EDC to prevent too large an injected fuel quantity if a fault should occur in the pedal travel transducer whereby the latter gives a signal corresponding to a substantially greater injectd fuel quantity than is desired by the driver.
Disadvantages of the supervisory systems described in U.S. Pat. Nos. 4,515,125 and 4,509,480 are that they cannot respond to all fault conditions and cannot pinpoint faults when they occur, for example, in the accelerator travel transducer.